Abstract: In order to study the effect of rockfall shape and size on the coefficient of restitution (COR), ten test blocks with different typical shapes and five test blocks with different sizes were adopted to conduct rockfall impact tests by a specially designed device. Based on the impact dynamics theory, the analysis of test results show that the normal COR (Rn) is very sensitive to the change of the block shape, and the Rn values of the non-angular shaped blocks are significantly higher than that of the angular shaped blocks. The Rn values of five non-angular shaped blocks are spherical > ellipsoid > cone with spherical base > cylinder > disk, and those of five angular shaped blocks are icosahedron > cube > tetrahedron > cuboid > triangle. Considering the geometric configuration and surface area distribution characteristics of the blocks, a new comprehensive shape quantification index-shape factor (?) is introduced, which has strong linear positive correlations with the Rn values of non-angular and angular shaped blocks respectively. Compared with Rn, the effect of the block shape on the tangential COR (Rt) is relatively weak, and the overall Rt values of the angular shaped blocks are slightly larger than that of the non-angular shaped blocks. Moreover, the size of the block has a significant impact on Rn and Rt. There are good linear negative correlations between the test block size and Rn and Rt. The rules obtained in this study provide important references for accurate prediction of rockfall disasters.

Key words: rockfall, shape, size, coefficient of restitution, shape factor